Homesickness is the feeling you have when you’re away from home and miss being there. What is it called when you are home, and miss someplace you’ve been to, e.g. when I miss being in Paris?
How about
[ul]
[li]Longing?[/li][li]Pining?[/li][li]Yearning?[/li][/ul]
Wanderlust?
Not quite what you’re looking for, but the opposite of homesickness is cabin fever.
I dunno what it’s called, but I live it every single day. 
I’m reminded of George Clooney’s character, Ryan Bingham, in “Up In The Air”. He defined “Home” as where he was most comfortable, so that he defined traveling as his “home”. The Airports, Airplanes and hotels were his home. When he had to go back to Omaha, was when he was homesick.
If you define home as where you are most comfortable, then there should no opposite of homesick.
It’s still homesick.
“Boy, am I homesick!”
“But you live at home.”
“Yeah, and I’m sick of it!”
2nd vote for wanderlust!
Hmmm…cabin fever means you just want to get out of where you are. Wanderlust is a desire to travel and explore, but isn’t specific to a particular location. What about pining, as in ‘pining for the fjords’?
*Why is it, when I am in Rome,
I’d give an eye to be at home,
But when on native soil I be
My soul is sick for Italy?
And why with you, my love, my lord,
Am I spectacularly bored,
But do you up and leave me, then
I scream to have you back again?*
- Dorothy Parker
Cabin fever sort of works.
No, cabin fever and wanderlust don’t refer to missing a particular place. I think “nostalgic” is the closest, as long as it can apply to places as well as times.
But the Norwegian Blue Parrot allegedly came from the fjords, so if it was “pining for the fjords”, it was homesick.
My vote is for “wanderlust” (an interesting example of a word taken directly from another language, but which looks like native English). But “cabin fever” is another kind of antonym which works in a way too.
I vote for wanderlust too!
Homesick mightn’t mean your actual home, it might mean your hometown or homeland.
Wanderlust might mean Paris, or Rome, or some other spot.
Cabin fever means “I gotta get out of here”. Particularly if others are at the core of the unhappiness.
Camp fever is about needing to get to deer camp.
Cabin fever is about needing to get out of the isolation of the cabin.
I’ve heard stories linking cabin fever and becoming a Wendigo.
I believe Wanderlust is the closest phrase to what you want.
It’s not pining, it’s passed on!
So what’s dance fever?
A movie silly. 